1. Technical Field
The present invention relates to audio amplifiers and more specifically to power supplies for audio amplifiers.
2. Background Art
Typically one of the last components in an audio distribution chain, audio amplifiers amplify a low power audio signal to a level suitable for driving a loudspeaker. As such, power gain is a major design factor for audio amplifiers. However, for a variety of reasons power supplies in audio amplifiers are not optimized for use in audio applications which results in unnecessary cost and increased size. This is particularly true of audio amplifiers employing switched-mode power supplies (SMPS) and class D amplification.
Under mandates in certain countries power supplies in electrical devices, including audio amplifiers, must meet minimum standards for power factor. A dimensionless number between zero (0) and one (1), power factor gives the ratio of real power to apparent power. The SMPS currently used in audio amplifiers cannot meet these standards without power factor correction (PFC). A common solution is to add a distinct PFC stage to the power supply.
Prior Art FIG. 1 is a block diagram of an illustrative power supply with power factor correction that is commonly employed in prior art amplifiers. The prior art power supply includes three separate circuits: a rectification circuit 11, a PFC correction circuit 13 and 12a conversion and isolation circuit. In this illustrative power supply, the power factor correction circuit 12 includes a boost regulator and is inserted between the rectification circuit 11 and the conversion and isolation circuit 13. The PFC circuit 12 receives a rectified direct current (DC) voltage from the rectifier circuit 11 and supplies a boosted DC voltage to the isolation and conversion circuit 13 at a voltage higher than the highest peak rectified voltage.
The addition of the power factor correction circuit 12 requires additional components which increase the cost and size of the power supply. Additionally, the second switching component in the PFC stage also introduces electromagnetic interference (EMI), which must be filtered out, as well as power conversion losses due to full power being converted two times.
There is now a need for an improved power supply that is optimized for use in an audio amplifier.